U.S. patent number 8,968,407 [Application Number 13/157,801] was granted by the patent office on 2015-03-03 for intervertebral disk implant.
This patent grant is currently assigned to Zimmer GmbH. The grantee listed for this patent is Guido Casutt, Michael Filippi, Mathias Heller, Jorn Seebeck. Invention is credited to Guido Casutt, Michael Filippi, Mathias Heller, Jorn Seebeck.
United States Patent |
8,968,407 |
Filippi , et al. |
March 3, 2015 |
Intervertebral disk implant
Abstract
The invention relates to an intervertebral disk implant having
two implant plates contacting prepared vertebral body surfaces in
the implanted state and an implant core which can be introduced
between the implant plates. The invention further relates to a
method for the manufacture of an intervertebral disk implant.
Inventors: |
Filippi; Michael (Schaffhausen,
CH), Heller; Mathias (Raeterschen, CH),
Seebeck; Jorn (Winterthur, CH), Casutt; Guido
(Rickenbach, CH) |
Applicant: |
Name |
City |
State |
Country |
Type |
Filippi; Michael
Heller; Mathias
Seebeck; Jorn
Casutt; Guido |
Schaffhausen
Raeterschen
Winterthur
Rickenbach |
N/A
N/A
N/A
N/A |
CH
CH
CH
CH |
|
|
Assignee: |
Zimmer GmbH (Winterthur,
CH)
|
Family
ID: |
35474912 |
Appl.
No.: |
13/157,801 |
Filed: |
June 10, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110238185 A1 |
Sep 29, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11107579 |
Apr 15, 2005 |
7959678 |
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Foreign Application Priority Data
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May 18, 2004 [DE] |
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10 2004 024 662 |
Nov 17, 2004 [EP] |
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04027322 |
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Current U.S.
Class: |
623/17.16 |
Current CPC
Class: |
A61F
2/4425 (20130101); A61F 2002/30604 (20130101); A61F
2002/30878 (20130101); A61F 2310/00796 (20130101); A61F
2230/0076 (20130101); A61F 2002/30563 (20130101); A61F
2002/30934 (20130101); A61F 2002/305 (20130101); A61F
2310/00023 (20130101); A61F 2002/30253 (20130101); A61F
2002/30565 (20130101); A61F 2002/30616 (20130101); A61F
2002/30841 (20130101); A61F 2002/302 (20130101); A61F
2002/30663 (20130101); A61F 2310/00029 (20130101); A61F
2002/30652 (20130101); A61F 2002/30662 (20130101); A61F
2002/443 (20130101); A61F 2002/30518 (20130101); A61F
2002/3065 (20130101); A61F 2002/30654 (20130101); A61F
2002/30937 (20130101); A61F 2230/0065 (20130101); A61F
2220/0025 (20130101) |
Current International
Class: |
A61F
2/44 (20060101) |
Field of
Search: |
;623/17.11-17.16 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
6369 |
|
Sep 2003 |
|
AT |
|
2031043 |
|
Nov 1971 |
|
DE |
|
2263842 |
|
Jul 1974 |
|
DE |
|
2804936 |
|
Aug 1979 |
|
DE |
|
3023353 |
|
Apr 1982 |
|
DE |
|
239523 |
|
Apr 1993 |
|
DE |
|
4213771 |
|
Sep 1993 |
|
DE |
|
29916078 |
|
Dec 1999 |
|
DE |
|
20310432 |
|
Oct 2003 |
|
DE |
|
20310433 |
|
Oct 2003 |
|
DE |
|
20313183 |
|
Nov 2003 |
|
DE |
|
20315611 |
|
Jan 2004 |
|
DE |
|
9542 |
|
Sep 2004 |
|
DE |
|
20320454 |
|
Oct 2004 |
|
DE |
|
176728 |
|
Jul 1989 |
|
EP |
|
560141 |
|
Oct 1996 |
|
EP |
|
560140 |
|
May 1998 |
|
EP |
|
699426 |
|
May 2000 |
|
EP |
|
955021 |
|
Sep 2001 |
|
EP |
|
1214918 |
|
Jun 2002 |
|
EP |
|
747025 |
|
Sep 2002 |
|
EP |
|
892627 |
|
Aug 2003 |
|
EP |
|
1344506 |
|
Sep 2003 |
|
EP |
|
1374807 |
|
Jan 2004 |
|
EP |
|
1437101 |
|
Dec 2004 |
|
EP |
|
1475059 |
|
Jan 2005 |
|
EP |
|
1346709 |
|
Dec 2005 |
|
EP |
|
1532948 |
|
Jun 2006 |
|
EP |
|
1405615 |
|
Oct 2006 |
|
EP |
|
1857079 |
|
Aug 2009 |
|
EP |
|
1549260 |
|
Jan 2010 |
|
EP |
|
2372622 |
|
Mar 1980 |
|
FR |
|
2718635 |
|
Jul 1996 |
|
FR |
|
2734148 |
|
Nov 1996 |
|
FR |
|
2730159 |
|
Apr 1997 |
|
FR |
|
2787017 |
|
Apr 2001 |
|
FR |
|
2775587 |
|
Oct 2001 |
|
FR |
|
2851157 |
|
Dec 2005 |
|
FR |
|
61122859 |
|
Jun 1986 |
|
JP |
|
63164948 |
|
Jul 1988 |
|
JP |
|
2003526456 |
|
Sep 2003 |
|
JP |
|
2004097823 |
|
Apr 2004 |
|
JP |
|
9310725 |
|
Jul 1993 |
|
WO |
|
9404100 |
|
Mar 1994 |
|
WO |
|
9519153 |
|
Jul 1995 |
|
WO |
|
9814142 |
|
Apr 1998 |
|
WO |
|
9905995 |
|
Feb 1999 |
|
WO |
|
9953871 |
|
Oct 1999 |
|
WO |
|
0004851 |
|
Feb 2000 |
|
WO |
|
0013619 |
|
Mar 2000 |
|
WO |
|
0042944 |
|
Jul 2000 |
|
WO |
|
0013620 |
|
Aug 2000 |
|
WO |
|
0053127 |
|
Sep 2000 |
|
WO |
|
0074606 |
|
Dec 2000 |
|
WO |
|
0101893 |
|
Jan 2001 |
|
WO |
|
0115638 |
|
Mar 2001 |
|
WO |
|
0119295 |
|
Mar 2001 |
|
WO |
|
0211650 |
|
Feb 2002 |
|
WO |
|
0193785 |
|
Apr 2002 |
|
WO |
|
0193786 |
|
Apr 2002 |
|
WO |
|
0247586 |
|
Jun 2002 |
|
WO |
|
02085227 |
|
Oct 2002 |
|
WO |
|
02085261 |
|
Oct 2002 |
|
WO |
|
02089701 |
|
Nov 2002 |
|
WO |
|
03003952 |
|
Jan 2003 |
|
WO |
|
03007779 |
|
Jan 2003 |
|
WO |
|
03007780 |
|
Apr 2003 |
|
WO |
|
03028583 |
|
Apr 2003 |
|
WO |
|
03032801 |
|
Apr 2003 |
|
WO |
|
03032802 |
|
Apr 2003 |
|
WO |
|
03063727 |
|
Aug 2003 |
|
WO |
|
03075804 |
|
Sep 2003 |
|
WO |
|
03084449 |
|
Oct 2003 |
|
WO |
|
03090650 |
|
Nov 2003 |
|
WO |
|
03094806 |
|
Nov 2003 |
|
WO |
|
2004026187 |
|
Apr 2004 |
|
WO |
|
2004028415 |
|
Apr 2004 |
|
WO |
|
2004037131 |
|
May 2004 |
|
WO |
|
2004039291 |
|
May 2004 |
|
WO |
|
2004041129 |
|
May 2004 |
|
WO |
|
2004041131 |
|
May 2004 |
|
WO |
|
2004047691 |
|
Jun 2004 |
|
WO |
|
2004016217 |
|
Jul 2004 |
|
WO |
|
2004054475 |
|
Jul 2004 |
|
WO |
|
2004054476 |
|
Jul 2004 |
|
WO |
|
2004054477 |
|
Jul 2004 |
|
WO |
|
2004054478 |
|
Jul 2004 |
|
WO |
|
2004066884 |
|
Aug 2004 |
|
WO |
|
2004073561 |
|
Sep 2004 |
|
WO |
|
2004084774 |
|
Oct 2004 |
|
WO |
|
2004089224 |
|
Oct 2004 |
|
WO |
|
2004089258 |
|
Oct 2004 |
|
WO |
|
2004089259 |
|
Oct 2004 |
|
WO |
|
2004098466 |
|
Nov 2004 |
|
WO |
|
2005072660 |
|
Aug 2005 |
|
WO |
|
Other References
European Patent Office, Partial European Search Report in related
Application No. 07008698.8-2310, dated Jul. 31, 2007 (8 pages).
cited by applicant.
|
Primary Examiner: Hoffman; Mary
Assistant Examiner: Carter; Tara R
Attorney, Agent or Firm: Seager, Tufte & Wickhem,
LLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a divisional of U.S. patent application
Ser. No. 11/107,579, filed Apr. 15, 2005, which is hereby
incorporated by reference in its entirety in the present
application.
Claims
What is claimed:
1. An intervertebral disk implant comprising: two implant plates
configured for contacting prepared vertebral body surfaces in the
implanted state; and an implant core configured to be introduced
between the two implant plates, the implant core made in multiple
parts, including an arrangement of at least one inner support
cushion and at least one shell surrounding the support cushion,
wherein the shell includes two half shells which are arranged
spaced apart from one another in an axial direction, wherein an
intermediate space is present in a radially outer rim region
between the shell and the support cushion, wherein at least one
implant plate has a spigot protruding from its inner side and which
projects into a depression formed on an outer side of the implant
core when the implant is assembled, with the depression being
dimensioned larger than the spigot in order to permit a relative
movement between the implant plate and the implant core.
2. An intervertebral disk implant in accordance with claim 1,
wherein the support cushion is substantially lens-shaped.
3. An intervertebral disk implant in accordance with claim 1,
wherein the support cushion and the shell are made from different
materials.
4. An intervertebral disk implant in accordance with claim 1,
further comprising an intermediate layer arranged between the
support cushion and the shell.
5. An intervertebral disk implant in accordance with claim 1,
wherein the implant core has a passage extending perpendicular to
an equatorial plane, the passage having a cross-sectional area
which varies over its length.
6. An intervertebral disk implant in accordance with claim 1,
wherein the support cushion has a ring shape.
7. An intervertebral disk implant in accordance with claim 1,
wherein the support cushion is stiffened in a central region in at
least one of an axial direction and a radial direction.
8. An intervertebral disk implant in accordance with claim 1,
further comprising a separate stiffening element which is arranged
in a passage extending perpendicular to an equatorial plane.
9. An intervertebral disk implant in accordance with claim 1,
wherein the support cushion, or an intermediate layer connected to
the support cushion, is connected to the shell by a clip, snap, or
latch connection.
10. An intervertebral disk implant in accordance with claim 1,
wherein the implant core is provided with an outer ring groove
and/or with an inner ring groove.
11. An intervertebral disk implant in accordance with claim 1,
wherein the implant core has a passage extending perpendicular to
an equatorial plane.
12. An intervertebral disk implant in accordance with claim 1,
wherein outer sides of the implant plates are each outwardly
arched.
13. An intervertebral disk implant in accordance with claim 1,
wherein the implant plates each have at least one guide
projection.
14. An intervertebral disk implant in accordance with claim 1,
wherein the spigot is arranged eccentrically with respect to a
dimension of the implant plate in the sagittal direction.
15. A method for the manufacture of an intervertebral disk implant,
comprising: providing two implant plates configured to contact
prepared vertebral body surfaces in the implanted state;
introducing an implant core between the implant plates, the implant
core including at least one inner support cushion and at least one
shell surrounding the support cushion and formed by two half
shells, wherein an intermediate space is present in a radially
outer rim region between the shell and the support cushion; and
wherein the inner support cushion is injection molded onto the
shell or onto an intermediate layer arranged between the support
cushion and the shell, wherein a material for the support cushion
is selected for the manufacture of a material composite between the
support cushion and the shell which has a higher melting point than
the material of the shell.
16. A method in accordance with claim 15, wherein the intermediate
layer is made from metal.
17. A method for the manufacture of an intervertebral disk implant,
comprising: providing two implant plates configured to contact
prepared vertebral body surfaces in the implanted state;
introducing an implant core between the implant plates, the implant
core including at least one inner support cushion and at least one
shell surrounding the support cushion and formed by two half
shells, wherein an intermediate space is present in a radially
outer rim region between the shell and the support cushion; and
wherein the inner support cushion is injection molded onto the
shell or onto an intermediate layer arranged between the support
cushion and the shell, wherein recesses or undercuts formed at an
inner side of the shell or the intermediate layer are injection
molded on the injection of the support cushion.
Description
TECHNICAL FIELD
The invention relates to an intervertebral disk implant and to a
method for its manufacture.
Artificial intervertebral disks have to satisfy a plurality of
demands and, in this process, do not only have to come as close as
possible to the behavior of a natural intervertebral disk, but
must, for example, also be usable in as simple a manner as
possible, i.e. must be able to be introduced between the respective
two adjacent vertebral bodies, and have to have good
biocompatibility with respect to the materials used. In particular
the reproduction of a resilient or dynamic behavior which is as
natural as possible under different pressure conditions, which
occur under the normal movements of the spinal column which also
bring about extreme strains, has proved to be difficult in the
design of intervertebral disk implants.
It is the object of the invention to provide an intervertebral disk
implant which satisfies all substantial demands in the best
possible manner and which in particular comes as close as possible
to a natural intervertebral disk with respect to the resilient or
dynamic behavior.
This object is satisfied by the features of claim 1 and in
particular in that the intervertebral disk implant includes two
implant plates, which contact prepared surfaces of intervertebral
bodies in the implanted state, as well as an implant core which can
be introduced between the implant plates.
Such an intervertebral disk implant provides a plurality of
possibilities to influence the dynamic or resilient behavior in the
respectively desired manner, for example by shaping or material
choice. The intervertebral disk implant in accordance with the
invention furthermore proves to be particularly advantageous with
respect to the introduction between two adjacent vertebral bodies.
Reference is made in this respect to the European patent
application EP 03 026 582 which was filed on Nov. 18, 2003 and
whose priority is claimed for the present application. This
priority application relates, among other things, to an operation
system for the insertion of intervertebral disk implants. This
operation system and the operation itself are, however, not the
subject of the present application so that they will not be looked
at in any more detail. Advantageous embodiments of the invention
can also be seen from the dependent claims, from the description
and from the drawing.
The implant core preferably has a lens-like basic shape. The
implant core can in particular have at least approximately the
shape of two spherical segments whose planar sides lie on top of
one another, with the respective spherical center of the one
spherical segment lying within the other spherical segment.
Alternatively, provision can be made for the implant core to have
at least approximately the shape of two spherical segments whose
planar sides face one another and of a cylindrical disk lying
between them, with--as in the aforesaid alternative--the spherical
center of the one spherical center lying within the other spherical
segment.
Investigations making use of model calculations have surprisingly
shown that local load peaks of the implant core can be avoided, in
particular while maintaining the rotational symmetry, if specific
adaptations of the geometry of the implant core are made. It has in
particular been found that the peak loads can be reduced by up to
30% with an implant core directly adapted with respect to the
geometry in comparison with an implant core whose articulation
surfaces are in full-surface contact with the articulation surfaces
of the implant plates when the implant has been assembled. Abrasion
effects and wear phenomena at the cooperating articulation surfaces
are hereby noticeably reduced.
It has in particular been found that the desired load reductions
can be achieved by an improved "spring effect" of the implant core
put under pressure via the implant plates.
Accordingly, in accordance with a preferred embodiment of the
invention, it is proposed that the implant core has a basic shape
of two spherical segments whose planar sides lie on top of one
another or face one another and is provided by material removal
from the basic shape with at least one spring region which gives
the implant core increased resilient shape changeability with
respect to the basic shape under the effect of pressure.
It is particularly preferred for the articulation surfaces of the
implant core and of the implant plates to contact one another in
linear or strip shape when the intervertebral disk implant is
assembled.
An advantage of such an embodiment lies in the fact that hollow
spaces filled with liquid between the outer surface of the implant
core and the counter surfaces of the implant plates, which are
sealed by a contact of implant core and implant plates, can bring
about or support an advantageous hydrostatic support effect in that
the effective support surface is expanded to the whole inner
region.
In a particularly preferred practical embodiment, the articulation
surfaces of the implant plates are each provided in the form of a
part surface of a sphere having a constant radius of curvature,
with the articulation surfaces of the implant core each being
formed by a plurality of part surfaces of a sphere having different
radii of curvature. The articulation surfaces of the implant plates
are preferably each formed by two part surfaces whose radii of
curvature are smaller than the radius of curvature of the
articulation surfaces of the implant plates and which start from a
contact line between the implant core and the implant planes in the
direction of the core pole, on the one hand, and in the direction
of the core equator, on the other hand.
Provision can alternatively or additionally be made for the implant
core to be provided, in particular in the region of its equatorial
plane, with an outer ring groove and/or with an inner ring groove
preferably forming a radial extension of a passage extending
perpendicular to the equatorial plane.
Spring regions likewise resulting in a reduction of peak loads are
created by such a material removal, on the basis of which the
implant core can be deformed in a directly pre-settable manner
under the effect of pressure.
It is preferred for the implant core to have a passage extending
perpendicular to the equatorial plane. The afore-mentioned load
calculations have shown that the peak loads can be reduced by the
explained measures irrespective of whether such a passage is
present or not. Nevertheless, such a passage provides a further
possibility of optimizing the implant geometry.
Complex investigations which make use of model calculations and
trials have furthermore shown that specific spatial distributions
of the resilience of the implant core prove to be particularly
advantageous. It can be achieved by a skilful choice of the
dependence of the resilient behavior or spring effect of the
implant core on the radial spacing to its center or central axis
that no unacceptably high specific pressure loads occur at any
point of the articulation surfaces of the implant core cooperating
with the articulation surfaces of the implant plates. It can in
particular be achieved that pressure peaks are avoided in the
radially outer region. In this manner, it is possible to
successfully counteract wear to the articulation surfaces which
brings along the risk of material abrasion to be avoided in every
case.
Provision is made in accordance with a preferred embodiment of the
invention for the implant core to have a greater resilience in a
radially outer rim region than in a radially inner central region.
Provision can furthermore be made for the implant core to have the
lowest resilience and thus the greatest stiffness in a radially
central region which is disposed between a radially outer region,
on the one hand, and a central region provided with a passage
extending perpendicular to an equatorial plane, on the other
hand.
In accordance with a particularly preferred embodiment of the
invention, the implant core is made in multiple parts. An
arrangement is in particular provided of at least one inner support
cushion and at least one shell surrounding the support cushion. The
support cushion can damp axial movements of the shell cooperating
directly with the implant plates. The support cushion can in
particular prevent disadvantageous pressure peaks in the radially
outer rim region and--where present--in the region of an inner side
bounding a central passage, for example by the manner of its inner
support or by its shape. This multi-part design has the advantage
that the arising of damaging abrasion is prevented or is at least
reduced by a sufficiently large amount even with materials used for
the implant core which have a comparatively low wear
resistance.
The support cushion preferably has a lens-shaped basic shape.
Provision is furthermore preferably made for the shell to include
two half shells which are preferably arranged spaced apart from one
another in the axial direction. Provision is furthermore preferably
made for the support cushion and the shell to be made from
different materials. The material of the shell is preferably harder
and/or stiffer than the material of the support cushion.
A particularly preferred material for the support cushion is
polycarbonate urethane (PCU). This material is particularly
well-suited to achieve a desired maximum "spring path" of the
implant core of approximately 1 mm. Alternatively, e.g. silicone or
a mixture of PCU and silicone correspondingly adjusted to the
desired resilient properties of the support cushion can also be
provided as the material for the support cushion.
Although it is in principle possible in accordance with the
invention to manufacture the implant core from a suitable material
such as in particular PCU, instead of having a multi-part design of
the implant core, and to prevent excessive pressure loads solely by
a skilful shape, in particular in the axial outer rim regions, it
is nevertheless preferred to, so-to-say, "enhance" the articulation
surfaces and, for this purpose, to use the mentioned shell
surrounding the support cushion at least partly or the half shells.
Polyethylene (PE), highly cross-linked polyethylene, UHMWPE
(UHMW=ultra-high molecular weight) or metal, in particular a CoCrMo
alloy or a titanium alloy, are preferably considered as the
material for the shell. The biocompatibility can in particular be
ensured by such materials.
If, in accordance with a further preferred embodiment, the support
cushion has its lowest resilience or its largest stiffness
approximately in the center between the radially outer rim region
and a central region, disadvantageous turning inside-out
arrangements of the half shells which are formed in ring shape on
the presence of a central passage can be avoided.
It is furthermore proposed in accordance with the invention for the
shell to project beyond the support cushion in the radial
direction. It is achieved by this "overhang" of the shell or of the
two half shells with respect to the inner support cushion that the
actual support of the implant plates is transposed via the shell or
half shells in the direction of a central region between the
axially outer rim region and a central region and, in this manner,
pressure peaks are prevented, or at least greatly reduced, in the
rim region or the central region.
In particular in the radially outer rim region of the implant core,
a respective intermediate space can be provided between the shell
or the half shells, on the one hand, and the support cushion, on
the other hand, such that no support of the shell at the support
cushion takes place in this region.
In accordance with a further embodiment of the invention, an
intermediate layer, in particular made of metal, is arranged
between the support cushion and the shell. The extent of this
intermediate layer can generally be selected as desired. The
intermediate layer can thus, for example, extend parallel to the
equatorial plane or be curved in accordance with the outer
shell.
If such an intermediate layer is present, which can consist of two
separate individual layers each associated with a half shell,
provision can then furthermore be made for the shell or the half
shells to be supported at the inner support cushion exclusively via
this intermediate layer or individual layers, i.e. material contact
takes place exclusively between the shell and the intermediate
layer, but not between the shell and the support cushion.
The intermediate layer can be made as a path boundary for spigots
of the implant plates projecting into a passage extending
perpendicular to an equatorial plane. An impairment of the outer
shell preferably consisting of PE is hereby avoided in an
advantageous manner.
Provision is furthermore preferably made for a passage of the
implant core extending perpendicular to an equatorial plane to have
a cross-sectional surface varying over its length. The
cross-sectional surface preferably respectively increases, in
particular constantly, from the equatorial plane to the outside.
The pressure behavior, in particular of the inner support cushion,
can be set directly by the shape of the central passage.
A further possibility of setting the pressure behavior of the
implant core lies, in accordance with a further preferred
embodiment of the invention, in the fact of stiffening the support
cushion in the axial direction in a central region. Alternatively
or additionally, the support cushion can be inwardly stiffened in
the radial direction in the event of the provision of a central
passage.
In particular a separate stiffening element, preferably having a
ring-shaped or cylindrical base shape, can be provided for the
stiffening of the support cushion. This stiffening element can be
arranged in the central passage and be made, for example, as
so-called metal bellows.
Such a stiffening element can not only increase the stiffness of
the support cushion in the central region or at the inner rim
region of the support cushion bounding the central passage, but can
simultaneously also support the support cushion in the radial
direction, whereby the stiffness of the support cushion in the
central region is likewise enlarged.
A stiffening element made, for example, as metal bellows moreover
offers the advantageous possibility to better guide the half shells
surrounding the support cushion at least in part and made in ring
shape in the case of a central passage, whereby a "floating" of the
half shells on the support cushion is avoided.
In a preferred embodiment of the invention, the support cushion is
injection molded onto the shell or the half shells, with the
material of the support cushion having a higher melting point than
the material of the shell, preferably for the forming of a material
composite between the support cushion and the shell which can be
established by the injection molding. The manufacture of the
intervertebral disk implant in accordance with the invention will
be looked at in more detail at another point.
Provision can also be made for the support cushion to be injection
molded onto the intermediate layer when an intermediate layer as
explained above is used.
It is furthermore proposed in accordance with the invention to
connect the support cushion or an intermediate layer connected to
the support cushion, and in particular made of metal, to the shell
or to the half shells by a clip, snap, or latch connection.
As regards the implant plates of the implant in accordance with the
invention, provision is preferably made in accordance with the
invention for the implant plates each to have a dome-shaped
extension, in particular in the shape of a spherical segment, or a
barrel-shaped extension on their outer side. These domes or barrels
provide a primary positional stability of the implant after the
insertion, with a barrel-shaped extension moreover being able to
satisfy a guide function during the insertion.
Furthermore, in accordance with the invention, it is proposed that
the outer sides of the implant plates are each outwardly arched.
These arches are preferably provided in addition to the
aforementioned dome-shaped or barrel-shaped extensions, and indeed
such that in each case the arch is shallower, but in contrast has a
larger extent in the plane of the plate than the dome or the
barrel.
Furthermore, provision can be made in accordance with the invention
for the outer sides of the implant plates each to have a planar rim
region extending at least over part of the periphery of the implant
plates.
Overall, a contour-optimized interface to the osseous composition
of the vertebral body can be achieved by an embodiment of the outer
sides of the implant plates in each case with a comparatively
strongly curved, dome-shaped or barrel-shaped extension, a
relatively shallow arch and a planar rim region.
Furthermore, the implant plates can each have at least one guide
projection, in particular formed as a peen, and/or a holding
projection, in particular a pyramid-shaped holding projection, on
their outer sides. The implant is hereby given rotational stability
in the inserted state, with the holding projections additionally
being able to give the inserted implant security against slipping
out. Provision is made in a particularly preferred embodiment for
the implant plates each to have a recess on their inner sides for
the reception of the implant core, with the cooperating
articulation surfaces of the recess and of the implant core each
being part surfaces of a sphere. The recesses permit a countersunk
arrangement, and so an arrangement secure against slipping out, of
the implant core between the implant plates. By forming the
articulation surfaces as part surfaces of a sphere, the
intervertebral disk implant in accordance with the invention is
rotationally symmetrical with respect to its movement
possibilities.
To reliably prevent a slipping out of the implant core from the
reception space formed by the recesses or concavities of the
implant plates with extreme body postures, provision can be made
for at least one implant plate to have a spigot which protrudes
from its inner side and which projects into a depression formed on
the outer side of the implant core when the implant is put
together, with the depression being dimensioned larger than the
spigot in order to permit a relative movement between the implant
plate and the implant core.
The spigot and/or the center of the implant core can be arranged
either centrally or eccentrically with respect to the dimension of
the implant plate in the sagittal direction.
To keep the required traction amount for the introduction of the
implant core between the implant plates as low as possible,
provision can be made in accordance with a further embodiment for
the implant core to be provided with an introductory passage for
the spigot of the implant plate extending from the margin to the
depression on at least one outer side.
An alternative or additional possibility to keep the traction
amount low consists, in accordance with a further embodiment, of
the fact of providing at least one implant plate--on its inner
side--with an introductory passage for the implant core extending
from the rim to the recess.
The invention also relates to a method for the manufacture of an
intervertebral disk implant which includes two implant plates
contacting prepared vertebral body surfaces in the implanted state
and an implant core which can be introduced between the implant
plates and includes at least one inner support cushion and at least
one shell surrounding the support cushion and preferably formed by
two half shells, with the support cushion being injection molded
onto the shell, in particular onto the half shells, in a plastic
injection molding method, or being injection molded onto an
intermediate layer arranged between the support cushion and the
shell in the finished state.
A material for the support cushion to be injection molded is
preferably selected for the manufacture of a material composite
between the support cushion and the shell which has a higher
melting point than the material of the shell. As already explained
above, a preferred material for the support cushion is
polycarbonate urethane (PCU), silicone or a mixture of PCU and
silicone, whereas polyethylene (PE), highly cross-linked PE, UHMWPE
or metal is preferably used for the shell. Whereas the melting
point of PCU lies above 200.degree. C., the melting point of PE
lies in the range of 120.degree. C. It was found that half shells
manufactured from PE can nevertheless be Injection molded from PCU
using a cooled injection mold such that a suitable material
composite is created.
This material composite can be improved in that recesses or
undercuts formed at the inner side of the half shells are filled on
the injection molding of the support cushion material.
The invention will be described in the following by way of example
with reference to the drawing. There are shown:
FIG. 1 different views of an intervertebral disk implant in
accordance with the invention;
FIGS. 2a+2b different perspective views of the intervertebral disk
implant of FIG. 1;
FIG. 2c an alternative embodiment of the intervertebral disk
implant of FIG. 1 with respect to the implant plates;
FIGS. 3a-3c in each case a plan view of an embodiment of an implant
core modified with respect to FIG. 1;
FIG. 4 a perspective view of an intervertebral disk implant
modified with respect to FIG. 1;
FIG. 5 a further embodiment of an intervertebral disk implant in
accordance with the invention;
FIG. 6 a further embodiment of an intervertebral disk implant in
accordance with the invention; and
FIGS. 7A-B, 8, 9A-C, 10A-B, 11A-C and 12A-B further embodiments of
an intervertebral disk implant in accordance with the
invention.
FIG. 1 shows different views of a possible embodiment of an
intervertebral disk implant in accordance with the invention which
includes two implant plates 15, 17 also designated as cover plates
or end plates as well as an implant core 19 also designated as an
inlay. As already mentioned in the introductory part, the insertion
of the intervertebral disk implant in accordance with the invention
will be not looked at in more detail in this application. The
likewise already mentioned European patent application EP 03 026
582 describes a spreading device in particular suitable for the
intervertebral disk implants in accordance with the Invention in
accordance with FIGS. 1 to 4 of which some components will be
mentioned in the following to the extent this is required for the
understanding of the implants described in FIGS. 1 to 4.
The implant core 19 has a lens-like base shape which corresponds to
two spherical segments contacting one another at their planar
sides. The outer articulation surfaces 49 of the implant core 19
are thus part surfaces of a sphere. As can in particular be seen
from the upper side view in FIG. 9, the shape of the implant core
19 does not precisely correspond to two spherical segments placed
on top of one another, but a spacer 18 of relatively low height and
with a straight rim is located between the planar sides of the
spherical segments.
The implant core 19 is provided at its poles with depressions 53
into which spigots 51 of the implant plates 15, 17 project, when
the implant is assembled, which will be considered in more detail
in the following.
As can in particular be seen from sections B-B and C-C, the implant
plates 15, 17 are each provided at their outer sides with a
relatively shallow arch 63 on which a more strongly curved
dome-shaped extension 41 in turn rises which corresponds to a
recess 45 on the inner side of the implant plate 15, 17 whose
articulation surface 47 is likewise a part surface of a sphere
whose radius corresponds to that of the articulation surfaces 49 of
the implant core 19. As in particular section C-C shows, there is
full-area contact between the two articulation surfaces 47, 49 in
the assembled state of the implant. For each spherical segment of
the implant core 19, the centre point M of the sphere, on whose
surface the articulation surfaces 47, 49 lie, lies within the
respectively other spherical segment, and indeed in the region of
the depression 53.
The implant plates 15, 17 are furthermore provided with peens 43 on
their outer sides. The implant plates 15, 17 are guided at these
guide projections 43 in groove-shaped recesses on the surfaces of
the vertebral bodies previously prepared by means of a ball-peen
hammer on insertion into the disk space.
Cut-outs 20 for the reception of an adapter element of a traction
shoe are formed opposite the peens 43 on the inner sides of the
implant plates 15, 17.
The variant in accordance with FIG. 2c differs from the implant
shown in FIG. 1 and FIGS. 2a and 2b by the design of the outer
sides of the implant plates 15, 17, which are here each provided
with a barrel-shaped extension 41', whereby--in the inserted
state--in turn a positional stability of the implant plates 15, 17
and additionally a longitudinal guidance is provided on the
insertion of the implant plates 15, 17.
Instead of e.g. peen-like guide elements, spike-shaped holding
projections 43' having a pyramid shape are moreover provided. The
height of these acutely tapering projections 43' also known as pins
is selected such that they do not disadvantageously influence the
insertion of the implant plates 15, 17, but provide positional
fixing, when the implant is inserted, in that they engage into the
vertebral body surfaces facing one another. An optimum insertion
behavior is achieved in that a respective edge of the
pyramid-shaped pins 43' faces in the direction of insertion. The
implant in accordance with FIG. 2c is designed for a different
surgical procedure and in particular for a different kind of
insertion of the implant plates 15, 17 and of their spreading than
the implant in accordance with FIG. 1 and FIGS. 2a and 2b. In
particular different instruments are used which will not be looked
at in more detail in the present application. Reference is made in
this respect to the European patent application EP 04 024 653 filed
on Oct. 15, 2004. The implant plates 15, 17 are each provided with
bores 44 on their ventral side for the reception of corresponding
projections of the setting devices for use with the instruments, in
particular setting units, described in the said application.
The diameter of the spigots 51 of the implant plates 15, 17
provided in the form of separate elements (section C-C in FIG. 1)
is smaller than that of the depressions 53 formed in the implant
core 19. The spigots 51, which project with clearance into the
depressions 53 in this manner, prevent the implant core 19 from
slipping out of the reception space formed by the two recesses 45
on extreme body postures.
As in particular the section A-A in FIG. 1 shows, the shallow
arches 63 on the outer sides of the implant plates 15, 17 in each
case do not extend over the total periphery up to the plate edge. A
planar rim region 65 extends over a partial periphery of the
implant plates 15, 17.
The section A-A moreover shows that the so-called angulation of the
implant plates 15, 17 is respectively measured with respect to a
zero frequency 0 which is a plane which extends perpendicular to
the center axes of the spigots 51 drawn as dashed lines. The
resulting angulation angle .alpha. of the assembled implant at a
specific relative position between the implant core 19 and the two
implant plates 15, 17 is determined by the sum of the caudal
angulation oc1 and the cranial angulation .alpha.2.
It can be seen from the plan view and from section A-A that the
center of the dome 41 and of the spigot 51 is eccentrically
displaced toward posterior along the center line.
The intervertebral disk implant in accordance with the invention
has specific characteristic values which can be varied on the
manufacture of the implant for the optimization of the implant and
for adaptation to the respective anatomy of the patient. These are
in particular the following parameters whose definition can be seen
from the respective different views of FIG. 1: H height of the
implant B width of the implant T depth of the implant R radius of
the articulation surfaces d dome position h dome height z arch
center w arch height a peen spacing f peen height v spacing of the
cut-outs
Corresponding parameters also exist analogously for the variant of
FIG. 2c in which consequently the respective parameters d and h
relate to the barrel 41' and the parameters a and f to the position
or to the spacing and to the height of the pins 43' and the
parameter v gives the spacing between the two outer bores 44 for
the insertion instrument.
In contrast to the embodiment shown in FIG. 1, the spigots 51 can
also be omitted. Such an alternative embodiment can in particular
be considered when the recesses 45 are made or can be made in the
implant plates 15, 17 such that they already provide sufficient
extrusion security alone, i.e. prevent the implant core 19 from
slipping out with adequate security.
The implant plates 15, 17 can be made from a CoCr alloy or from a
titanium alloy and be coated on the outer bone side with porous
titanium and, optionally, also with hydroxyapatite (HAC) in order
to permit a particularly fast ongrowth of the bone in this manner.
In practice, a set of differently sized implant plates 15, 17 is
preferably available to achieve optimum matching to different
patient anatomies. The implant plates 15, 17 can in particular
differ from one another with respect to their width, depth and
angulation.
The implant core 19 can consist, for example, of polyethylene,
highly cross-linked PE, UHMWPE or metal, in particular a CoCrMo
alloy.
Polyethylene is the preferred material, since hereby axially acting
forces can be absorbed better resiliently, i.e. a better axial
damping property is present. To avoid any possible abrasion, a thin
metallic shell can be laid over the plastic material. A combination
of metallic part surfaces of a sphere then arises which can be
manufactured in enormously high precision with respect to one
another due to their spherical form. Such a metal/metal interplay
is generally described in the European patent application
97903208.3 (publication number EP 0 892 627) to whose content
reference is explicitly made to complement the disclosure of the
present application.
By the countersunk arrangement of the implant core 19 in the
concavities 45 of the implant plates 15, 17, a relatively large
force transmission area is provided and thus a comparatively small
surface load is achieved, with the risk of extrusion simultaneously
being kept low.
The perspective representations of the implant in FIGS. 2a and 2b
in particular show the cut-outs 20 formed on the inner sides of the
implant plates 15, 17 for the traction shoes and the design of the
outer sides of the implant plates 15, 17 with the dome 43 and the
peens 43.
FIGS. 3a-3c and FIG. 4 show possible measures which can be taken at
the implant core 19 (FIGS. 3a-3c) and at the inner sides of the
implant plates 15, 17 (FIG. 4) in order to keep the degree by which
the implant plates 15, 17 have to be pressed apart for the
introduction of the implant core 19 as low as possible.
In accordance with FIGS. 3a-3c, an introduction passage 55 is
formed in each case on the outer side of the implant core 19
extending from the rim of the implant core 19 up to the central
depression 53. The introduction passage 55 can generally have an
extent of any desired curvature and open either substantially
radially (FIG. 3a) or tangentially (FIG. 3b) into the depression
53. Alternatively, the introduction passage 55 can have a
straight-line radial extent (FIG. 3c).
On the introduction of the implant core 19 between the implant
plates 15, 17, the spigots 51 project into the introduction
passages 55 of the implant core 19 so that the spigots 51 are also
not in the way of an implant core 19 to be introduced with a lower
plate spacing. Alternatively or additionally to the introduction
passages 55 of the implant core 19, the implant plates 15, 17 are
each provided on their inner sides with an introduction passage 57
in the form of a groove-like depression which extends from the
anterior plate rim up to the recess 45, whereby in total an
"introduction tunnel" for the implant core 19 is present which
extends from the anterior side up to the reception space for the
implant core 19. The implant core 19 has already partly been
received in the introduction passages 57 at the start of the
introduction process so that the implant plates 15, 17 have to be
pressed apart from one another by less much.
On an operation for the insertion of the intervertebral disk
implant in accordance with the invention, the preparation of the
disk space takes place up to the time at which the operation system
in accordance with the invention comes into use, as previously,
i.e. the scraping of the natural intervertebral disk takes place
without the operation system in accordance with the invention. A
first preparation of the end plates of the vertebral bodies also
takes place in particular with a so-called "sharp spoon" (e.g.
Cobb) without using the work plates 11, 13 in accordance with the
invention.
Subsequently to this first preparation of the disk space, an
operation system can be used, for example, such as is described in
the aforementioned European patent application EP 03 026 582.
FIGS. 5 and 6 show preferred embodiments for an intervertebral disk
implant in accordance with the invention. It is common to both
embodiments that the articulation surfaces 147 of the implant
plates 115, 117 are each part surfaces of a sphere with a radius R0
and a center MO lying on the center axis 167 of the implant and on
a spigot 151 of the respectively other plate. Both implant cores
119 are moreover each made rotationally symmetrically and are
provided with a central passage 173 whose longitudinal axis
coincides with the center axis 167.
In the implant core 119 in accordance with FIG. 5, the articulation
surfaces 149 are likewise part surfaces of a sphere with a radius
R0 and a center MO in accordance with the articulation surfaces 147
of the implant plates 115, 117 so that--analogously to the implant
in accordance with FIG. 1--the articulation surfaces 147, 149 of
the implant core 119 and of the implant plates 115, 117 contact one
another over a full area.
In order to achieve an improved "spring effect" for the
minimization of peak loads under the influence of pressure, as is
explained in the introductory part, the implant core 119 is
provided at the height of the equatorial plane with an outer ring
groove 169 and an inner groove nut 171 which is substantially wider
in comparison with the outer ring groove 169 and which in this
respect represents a radial extension of the central passage
173.
In the implant core 119 in accordance with FIG. 6, a different
approach was selected to achieve an improved support effect. The
articulation surfaces 149 of the implant core 119 are here not part
surfaces of a sphere shaped in accordance with the articulation
surfaces 147 of the implant plates 115, 117. It is rather the case
that the articulation surface 149 of the implant core 119 is shaped
in each quadrant such that the implant core 119 and the implant
plates 115, 117 only touch at a line P. In the cross-section shown
here along the center axis 167, the position of the contact line P
is selected such that a straight line extending through the center
MO and the point P, that is intersecting the tangent t through the
point P at right angles, includes an angle to with the equatorial
plane of the implant core 119 which amounts to approximately
60.degree.. The angle a> preferably lies in an angular range
from approximately 45.degree. to 75.degree..
FIG. 6 shows two preferred variants on the basis of this basic
principle of a line contact between the implant core 119 and the
implant plates 115, 117. In the variant shown with solid lines, the
articulation surface 149 of the implant core 119 has a constant
radius of curvature R1<RO with a center M1. A variant is shown
by the double chain-dotted line in FIG. 6 in which, starting from
the contact line P, the curvature of the articulation surface 149
of the implant core 119 is larger in the direction of the core pole
than in the direction of the core equator, i.e. the radius of
curvature R2 with the center M2 is smaller than the radius of
curvature R1 with the center M1.
A preferred condition for these parameters is RO-6 mm<R1<RO-1
mm, where R2<R1 and 8 mm<RO<18 mm.
In accordance with FIG. 6, provision is furthermore made in this
embodiment for the centers MO, M1 and M2 to lie on a common
straight line which intersects the contact line P marking the
transition between the two articulation surface regions of the
implant core 119.
In accordance with the invention, a combination of the specific
articulation surface geometry in accordance with FIG. 6 with the
ring groove approach in accordance with FIG. 5 is also basically
possible, i.e. different measures which each result in a geometry
of the implant core differing from a simple base shape can
generally be combined with one another to achieve an improved
"spring effect".
The implant cores described in this application and in particular
in the following in connection with FIGS. 7 to 12 are in particular
coordinated to an average central European with respect to their
dimensions. The implant cores have a lens-shape with an outer
diameter of approximately 25 mm and a height of approximately 19 mm
which is provided by the flattening of a central passage extending
in the axial direction. Furthermore, the implant cores are designed
for a radius of curvature RO of approximately 14 mm of the implant
plates not shown in FIGS. 7 to 12.
It is furthermore common to all implant cores that the articulation
surfaces of the implant core cooperating with articulation surfaces
of the implant plates are part surfaces of a sphere with the
mentioned radius of curvature RO of approximately 14 mm. The lens
shape of the implant cores is self-aligning in that the implant
cores have at least approximately the shape of two spherical
segments whose planar sides face one another, with the respective
spherical center of the one spherical segment lying inside the
other spherical segment.
The implant core in accordance with FIGS. 7a and 7d includes an
approximately lens-shaped support cushion 277 on which two
half-shells 279, 281 lying spaced apart from and opposite to one
another are arranged. The support cushion 277 consists of
polycarbonate urethane (PCU), silicone or a PCU/silicone mix,
whereas the two half shells 279, 281 are manufactured from
polyethylene (PE), highly cross-linked PE, UHMWPE or metal, in
particular a CoCrMo alloy. Both the support cushion 277 and the two
half shells 279, 281 each had a ring shape due to a passage 273
which extends perpendicular to the equatorial plane 275 and whose
center axis coincides with the center axis 267 of the implant core
219.
The half shells 279, 281 project beyond the support cushion 277 in
the radial direction. In the region of this overhang or of this
covering, a ring gap is present between the half shells 279, 281
axially spaced apart in this respect which forms a radially outer
ring groove 269 of the implant core 219. This ring groove 269 can
in particular be recognized in the perspective representation of
FIG. 7b.
The articulation surfaces 249 of the implant core 219 formed by the
outer sides of the half shells 279, 281 are part surfaces of a
sphere and have the same radius of curvature as the articulation
surfaces of the implant plates (not shown) of the intervertebral
disk implants.
The radially outer side edge of the support cushion 277 extends
parallel to the center axis 267, whereas the inner rim or inner
side of the support cushion 277 bounding the central passage 273 is
made in convex shape. This extent of the inner side of the support
cushion 277 is continued by the inner rim region of the half shells
279, 281. The central passage 273 consequently has a shape in the
axial section shown here of a double cone, a double funnel or an
hourglass with a minimal free inner cross-sectional area in the
equatorial plane 275.
Spigots of the implant plates project into the central passage 273
in the assembled state of the intervertebral disk implant, e.g.
corresponding to the embodiments of FIGS. 5 and 6.
The support cushion 277 and the two half shells 279, 281 form a
solid material composite which is manufactured by injection molding
of the material used for the support cushion 277 (in particular
PCU, silicone or a PCU/silicone mix) onto the half shells 279, 281
consisting in particular of PE highly cross-linked PE, UHMWPE or
metal, in particular a CoCrMo alloy, as is described in the
introductory part.
Thanks to its lens shape, the support cushion 277 provides a softer
support for the half shells 279, 281 in its central range in the
axial direction than in the radially outer rim region. This
behavior can be influenced by the shape of the central passage 273.
The actual support is transposed radially inwardly by the mentioned
radial overhang of the half shells 279, 281, whereby the occurrence
of pressure peaks in the radially outer rim region is avoided.
The implant core 219 in accordance with FIG. 8 differs from that of
FIGS. 7a and 7b by the provision of an outer ring groove 285 formed
in the support cushion 277 at the height of the equatorial plane
275. The extent of the reduction of the axial height of the support
cushion 277 in the radially outer rim region can be set by such a
restriction.
The ring groove 285 of the support cushion 277, together with the
equatorial ring gap between the two half shells 279, 281, forms the
outer ring groove 269 of the total implant core 219.
In the implant core 219 in accordance with the invention shown in
FIGS. 9a-9c, the support cushion 277 terminates in a respectively
flush manner downwardly and upwardly with a ring shaped
intermediate layer 289, 291 made of metal. The outer diameter of
the intermediate rings 289, 291 extending parallel to the
equatorial plane 275 amounts to approximately 60% of the outer
diameter of the outer PE half shells 279, 281, whereas the inner
diameter of the intermediate rings 289, 291 amounts to
approximately 24% of the outer diameter of the half shells.
In each case starting from the ring shaped intermediate layers 289,
291, the diameter of the support cushion 277 increases in the
direction of the equatorial plane 275, with a respective
intermediate space 283 becoming outwardly wider, however, being
present radially outside the intermediate layers 289, 291 between
the support cushion 277 and the half shells 279, 281. The half
shells 279, 281 are consequently only supported via the metal rings
289, 291 at the support cushion 277.
The support cushion 277 forms, with the metal intermediate rings
289, 291, a solid material composite which is manufactured at the
inner sides of the intermediate layers 289, 291 by injection
molding of the material provided for the support cushion 277 for
which e.g. the aforesaid materials are considered. An additional
shape-matched connection is created by undercut bores 295 which are
formed in the intermediate layers 289, 291 and into which the
material of the support cushion 277 flows during manufacture. As
FIG. 9c shows, a plurality of circular undercuts 295 are provided
which are arranged at a uniform spacing from one another.
As the detail "C" of FIG. 9a shows, the side edges of the
intermediate rings 289, 291 and the radially outer bounding sides
of reception regions formed in the half shells 279, 281 are
undercut such that a respective snap-connection can be established
between the composite of support cushion 277 and intermediate rings
289, 291, on the one hand, and the two half shells 279, 281, on the
other hand. The half shells 279, 281 can therefore simply be
clipped onto the support cushion 277 fixedly connected to the metal
rings 289, 291.
In the embodiment of FIGS. 10a and 10b, ring-shaped intermediate
layers 289, 291 are in turn arranged between the support cushion
277 made of PCU and the PE shells 279, 281. In this embodiment, the
intermediate rings 289, 291 do not, however, extend perpendicular
to the center axis 267 of the implant core 219, but are rather
curved in accordance with the outer half shells 279, 281 providing
the articulation surfaces 249.
The radial inner side of the ring-shaped support cushion 277 has a
comparatively strong convex curvature, with the central passage 273
having a pronounced narrowing in the equatorial plane 275.
In the radial direction, the support cushion 277 terminates in a
flush manner with the intermediate rings 289, 291 via a flange-like
section 287 lying between the intermediate metal rings 289, 291.
The PE half shells 279, 281 therefore in turn have an overhang with
respect to the composite of support cushion 277 and intermediate
rings 289, 291. The half shells 279, 281 each terminate in the
axial direction in a flush manner with the intermediate rings 289,
291, whereby the implant core 219 has an outer ring groove 269
whose axial height corresponds to the thickness of the flange
section 287 of the support cushion 277.
The connection between the intermediate layers 289, 291 made from a
CoCrMo alloy and the PE half shells 279, 281 takes place in each
case by injection molding of the PE material onto the outer sides
of the metal intermediate layers 289, 291 which are provided for
this purpose with recesses or undercuts (not shown in FIG. 10a)
into which the PE material can flow during injection molding. These
undercuts are preferably provided in the form of circular, recessed
steps whose width and height vary with the radial position such
that the step width reduces and the step height increases from the
inside to the outside. This manufacture of the material composite
can basically also be used with other material pairs, that is it is
not limited to PE for the half shells and a CoCrMo alloy for the
intermediate layers.
It is preferred for the embodiments of FIGS. 9 and 10 for the
spigots (cf. FIGS. 5 and 6) projecting from the implant plates (not
shown here) and protruding into the central passage 273 to extend
up to the metallic intermediate layers 289, 291 since then, with
tilt movements of the implant plates taking place relative to the
implant core 219 due to the articulation, the metal rings 289, 291
can serve as path boundaries for the spigots and thus the implant
plates without impairing the PE half shells 279, 281.
The implant core 219 in accordance with FIGS. 11a, 11b does not
have any intermediate layers between the support cushion 277 again
made of PCU and the outer half shells 279, 281 which are not made
of PE in this embodiment, but of metal. The connection between the
PCU support cushion 277 and the half shells 279, 281 takes place by
injection molding of the PCU material.
At its radial inner side, the support cushion 277 is supported by a
stiffening element 293 which is made as metal bellows and which
extends up to the inner sides of the metal half shells 279, 281. On
the one hand, the stiffness of the support cushion 277 in the axial
direction is hereby increased. On the other hand, an improved guide
of the half shells 279, 281 relative to one another results due to
the stiffening element 293, whereby it is prevented that the half
shells 279, 281 "float" on the support cushion 277.
The half shells 279, 281 and the stiffening element 293 are
preferably made from the same material for which in particular a
CoCrMo alloy is used.
The wall thickness of the half shells 279, 281 lies in an order of
approximately 1 mm, whereby sufficient shape resilience results. A
resulting support of the half shells 279, 281 in the central region
between a radially outer ring groove 285 of the support cushion 277
and the inner side, i.e. the stiffening element 293, permits a
comparatively small change of shape of the half shells 279, 281 in
the radially outer rim region in the order of \xm in the axial
direction.
The outer ring groove 285 of the support cushion 277 and the ring
gap between the half shells 279, 281 axially spaced apart in this
respect together form an outer ring groove 269 of the total implant
core 219. An inner ring groove 271 is created by a radially
outwardly directed bulging of the metal bellows 293 at the height
of the equatorial plane 275.
The articulation surfaces 249 (formed by part surfaces of a sphere)
of the half shells 279, 281 made of metal in this embodiment and
the corresponding articulation surfaces of the implant plates (not
shown) can be processed--when the spigots of the implant plates
(cf. e.g. FIGS. 5 and 6) are subsequently attached to the implant
plates e.g. by pressing in--by means of the method already
mentioned in the aforesaid European patent application with the
publication number EP 0 892 627 with that precision which is
required to achieve the desired reduction in the surface pressing
in these rim regions via the shape resilience of the radially outer
rim regions of the half shells 279, 281.
Alternatively to the embodiment shown in FIGS. 11a and 11b, in
accordance with a further variant of the invention shown in FIG.
11e, the support cushion can also be omitted and the support of the
half shells 279, 281 can take place exclusively via a stiffening
element 293', e.g. corresponding to the bellows 293 in accordance
with FIG. 11a. In this variant, the stiffening element 293' is
offset radially outwardly, i.e. provided with a larger diameter,
with respect to the position shown in FIG. 11a. As a result, the
support of the half shells 279, 281 takes place in a central
region--in which the half shells 279, 281 each have an axial ring
projection for the stiffening element 293'--between the radially
outer margin, on the one hand, and the inner margin bounding the
central passage 273 or the central openings of the ring-shaped half
shells 279, 281, on the other hand, whereby pressure peaks are in
turn avoided in these radially outer and inner rim regions.
In the embodiment of FIGS. 12a and 12b, the implant core 219 is
only formed by a PCU support cushion which is provided with a
central passage 273 symmetrical to the equatorial plane 275 in the
form of a double cone converging in the equatorial plane 275.
The implant core 219 has the shape of two spherical segments whose
planar sides face one another and a cylindrical disk 218 disposed
therebetween. The axial height of this cylindrical disk 218 is
selected such that the part surfaces of a sphere (not shown) of the
implant plates cooperating with the articulation surfaces 249 of
the implant core 219 cover the cylinder disk 218, i.e. still have a
sufficiently large overhang, in every permitted articulation
position.
Compression takes place under load due to the comparatively high
resilience of the PCU material forming the implant core 219 not
only in the axial direction, but also in the radial direction,
whereby the axially outer rim region of the articulation surfaces
249 is reduced. A reduction of the pressure load of the
articulation surfaces 249 in the direction of the axially outer rim
regions consequently also occurs with coinciding radii of curvature
RO between the implant core 219 and the implant plates.
The pressure distribution adopted under load can also be set
directly toward the radially inner side by the shape of the central
passage 273 which is of double cone shape here.
The articulation surfaces 249 of the PCU implant core 219 can
additionally be provided with a cross-link and/or a coating which
serves to reduce the wear. In this process, the wear reduction can
be achieved by a higher strength and/or by a lower friction
value.
The implant cores 219 explained above with reference to FIGS. 7 to
12 have the following dimensions, with reference moreover being
made to the introductory part in this respect:
The smallest inner diameter of the ring-shaped support cushion 277,
i.e. the diameter of the central passage 273 at the narrowest
restriction disposed in the equatorial plane 275 amounts to
approximately 5 mm in the examples of FIGS. 7, 8 and 9, to
approximately 0.4 mm in the example of FIG. 10 and to approximately
4 mm in the example of FIG. 12.
The largest diameter of the central passage 273 at the outer side
of the half shells 279, 281 or of the implant core 219 amounts to
approximately 7.4 mm in the examples of FIGS. 7 and 8 and to
approximately 7.3 mm in the example of FIG. 12.
The spacing between the centers of the spherical segments defining
the part surfaces of a sphere 249 amounts to approximately 6 mm in
the examples of FIGS. 7, 8 and 11 and to approximately 5 mm in the
example of FIG. 12.
The opening angle of the central passage 273 at the outer side of
the half shells 279, 281 amounts to approximately 20.degree. in the
examples of FIGS. 7 and 8.
The axial height of the radially outer ring gap between the half
shells 279, 281 amounts to approximately 2 mm in the examples of
FIGS. 7, 8 and 10. In the example of FIG. 11, the smallest spacing
between the half shells 279, 281 and thus the maximum axial width
of the outer ring groove 285 of the support cushion 277 (FIGS. 11a
and 11b) amounts to approximately 2.6 mm.
In the example of FIG. 9, the axial spacing between the metal rings
289, 291, i.e. the axial height of the support cushion 277, amounts
to approximately 8 mm and the diameter of the central passage 273
at the height of the outer sides of the metal rings 289, 291
amounts to approximately 6 mm. The thickness of the metal rings
289, 291 amounts to approximately 1 mm.
In the example of FIG. 10, the wall thickness of the ring-shaped
intermediate layers 289, 291 amounts to approximately 1.7 mm. The
diameter of the central passage 273 at the maximum axial height of
the support cushion 277, i.e. the smallest diameter of the
intermediate rings 289, 291, amounts to approximately 6 mm.
In the example of FIGS. 11a and 11b, the inner diameter of the
stiffening element 293 amounts to approximately 6.7 mm, whereas its
wall thickness--also in the example of FIG. 11c--amounts to
approximately 0.5 mm.
REFERENCE NUMERAL LIST
15, 115 implant plate 17, 117 implant plate 18, 218 intermediate
disk 19,119,219 implant core 20 cut-out for the adapter element 41,
41' dome shaped or barrel shaped extension 42 abutment pin 43, 43'
guide projection, peen or holding projection 44 bore 45 recess of
the implant plate 47, 147 articulation surface of the recess or
implant plate 49, 149, 249 articulation surface of the implant core
51, 151 spigot 53 cut-out 55 introduction passage of the implant
core 57 introduction passage of the implant plate 59 fluid line 61
vertebral body 63 arch 65 rim region M spherical center R radius of
the articulation surfaces 0 zero reference .alpha. angulation H
height of the implant plates B width of the implant plates T depth
of the implant plates d dome position h dome height z arch center w
arch height a peen spacing f peen height v spacing of the cut-outs
167, 267 center axis of the implant core 169, 269 outer ring groove
171, 271 inner ring groove 173,273 central passage M0, M1, M2
center R0, R1, R2 radius of curvature P contact line t tangent
.omega. angle 275 equatorial plane 277 support cushion 279 half
shell 281 half shell 283 intermediate space 285 outer ring groove
of the support cushion 287 flange section of the support cushion
289 intermediate layer 291 intermediate layer 293, 293' stiffening
element 294 ring projection 295 recess, undercut
* * * * *